CAN SCREENING CRITERIA FOR DROUGHT RESISTANCE IN NICOTIANA-TABACUM-L BE DERIVED FROM THE POLYPHASIC RISE OF THE CHLOROPHYLL-A FLUORESCENCE TRANSIENT (OJIP)
L. Vanrensburg et al., CAN SCREENING CRITERIA FOR DROUGHT RESISTANCE IN NICOTIANA-TABACUM-L BE DERIVED FROM THE POLYPHASIC RISE OF THE CHLOROPHYLL-A FLUORESCENCE TRANSIENT (OJIP), South African journal of botany, 62(6), 1996, pp. 337-341
Four tobacco cultivars (Nicotiana tabacum L.), known to differ with re
spect to their drought resistance, were subjected to a slowly intensif
ying drought stress (control level: psi(PD) = ca. -0.5 MPa; and severe
stress level: psi(PD) = ca. -2.5 MPa), and rewatered under controlled
environmental conditions in programmable growth rooms. Drought stress
-induced changes in the fast-phase chlorophyll fluorescence induction
kinetics during the stress and recovery periods were monitored with a
shutterless fluorescence measuring system with a time resolution of 10
mu s (Plant Efficiency Analyser by Hansatech Instr., UK). Although ch
lorophyll fluorescence transients are excellent probes for measuring t
he effects of stress on the PSII photo-chemistry, in this article we e
valuate their practical applicability in screening for drought resista
nce. During the entire drought stress and recovery period, the fluores
cence transients followed a regular pattern of O-J-I-P--T, with two in
termediate inflections J (ca. 2 ms) and I (ca. 20 ms) appearing betwee
n the F-o and F-m levels. From the fluorescence data presented, it is
clear that the single fluorescence parameter which differed the most i
n its response to drought stress between the drought-resistant (GS46 a
nd ELSOMA) and drought-sensitive (TL33 and CDL28) cultivars was the F-
o value normalized to F-o (t=o), which in confirmation of their drough
t resistance, increased dramatically in the former but not in the latt
er cultivars. In the interpretation of the results, however, care is e
xpressed not to attempt to correlate changes observed in individual tr
ansient components with possible physiological causes, since these ind
ividual fluorescence parameters are influenced by an array of interact
ing physico-chemical and metabolic factors. The use and importance of
normalized values, ratios and indices, in terms of the practical appli
cation of chlorophyll fluorescence measurements in drought-stress rese
arch is discussed.